The didemnins (A, B, C, D, E, X and Y) are members of a novel class of cyclic depsipeptides isolated from the Caribbean tunicate Trididemnum solidum (family Didemnidae). See, Rinehart, K.L., et al., J. Nat. Prod., 1988, 51, 1.
These peptides exhibit a wide variety of biological activities both in vivo and in vitro including antiviral, antitumor, antiproliferative and immunosuppressive activities.